Inbreeding

As far as the AKC is concerned, the relationship between the Sire and Dam of the litter has no bearing on registration eligibility. Anyone who considers breeding their dog must consider temperament, health, and finding mates that complement each other. Breeding dogs that are closely related can fix certain characteristics, both desirable and undesirable. Therefore, it is expect by the AKC that only very experienced breeders would consider inbreeding and line breeding. However, there is no rule that prohibits inbreeding and line breeding; this is left to the discretion of individual breeders.

Different breeders will give you different responses as to how close is too close when breeding. Most breeders, however, agree that parent to child is too close. However, many of these same breeders do linebreed, which is condoned by both the AKC and the DPCA. There are also varying opinions about what constitutes linebreeding. Linebreeding is simply descriptive of inbreeding on animals a little further back in the pedigree than child and parent. Inbreeding is popularly thought to be the mating of relatives, which is too general a definition. If we look at the pedigree of any individual we find that ancestors double in each generation. We have two parents, four grandparents, eight great grandparents etc. In any lineage, the time will come when there are more ancestors in a pedigree generation than there are individuals alive at that time. It might be possible, in a numerically large breed, to find nothing in common within five generations. However, the further back one goes there will be ancestors that appear several times. Therefore, one cannot define inbreeding as simply mating relatives. At best, the definition should probably be defined as "the mating of individuals more closely related than the average of the population from which they come". A true definition of inbreeding could vary from breed to breed and from location to location. However absolute values can be derived and assessed on that count.

Inbreeding is measured using Wright's Coefficient of Inbreeding, which was first put forward in the 1920s. It can be expressed as a percentage e.g. 12.5% or as a proportion 0.125. It measures the increased homozygosity likely to occur in an individual. If you mate a Doberman to a Doberman you get Dobermans which is no surprise because many genes have become fixed in the breed. This means that all individuals carry the same combination of these genes. Whether we inbreed or not, it would make no difference to genes that are fixed in all members of the breed, but in non-fixed genes it would lead to an increase in homozygosity and a decrease in heterozygosity. Thus, linebreeding is simply descriptive of inbreeding a little further back in the pedigree..

Most deleterious traits tend to be recessive. If an undesirable feature is dominant, any individual that demonstrates it is usually not selected for purposes of future breeding, unless it has a very late onset and is not detected prior to breeding. Additionally, many rare genes may be lost on inbreeding depending on the population. Thus inbreeding does not operate in isolation but is coupled with selection. This this is certainly true with respect to inherited defects. However, if a line does not carry a specific defect, inbreeding will not create it.

Consider, for example, Von WilleBrandt's Disease (vWD), a disorder much like hemophilia which results in heavy bleeding when defective genes involved in blood clotting have been inherited. In order to create a breed of dog, you usually inbreed dogs that have particular characteristics until they produce uniform offspring. This is why all German Shepherds or Dalmatians or Doberman Pinchers look similar. They are inbred. If one of the parent dogs that you started your inbreeding efforts with had a defective gene, their offspring will have a high chance of inheriting two copies of that gene. In the case of vWD, the three dog breeds (Shelties, Scottish Terriers, and Doberman Pinschers) each have a different type of defective version of the gene responsible for vWD. Those defective genes probably came from the dogs that started those breeds, and all of the dogs in that breed are closely related to each other because they are inbred. In order for the defect to cause the disease to be displayed, a Doberman must inherit both defective genes for vWD, one from each parent. A Doberman with both defective genes for vWD is called "affected" and may demonstrate the heavy bleeding trait. A Doberman with only one of these defective genes is called a "carrier" and, like a Doberman with neither gene being defective, called a "clear", will show no signs of the disorder.

For example, assume a line which began with a Doberman who was the offspring of a Von WilleBrandt's Disease (vWD) "carrier" with the second parent being a vWD "clear". This would mean that our Doberman could never demonstrate the heavy bleeding trait. It would have a 50:50 chance that it might carry one vWD gene as a "carrier" and a 50:50 chance that it would be a "clear". It is good to remember that breeders, even if they inbreed, may also follow positive selections. So that we are not just talking about inbreeding but inbreeding with selection, which is a different ball game. The belief that inbreeding always causes problems is too sweeping. If there is no dominance there is no depression for a trait. The critics of inbreeding rarely, if ever, tell you this. Inbreeding will not have much effect upon high heritability traits but could have with respect to low heritability traits.

As more research into inbreeding and genetic diversity is carried out, the more evidence mounts that artificial selection is deleterious and natural selection results in a much broader diversity and therefore greater health safety level. Even in Germany, where breeders formerly prided themselves on keeping “open” at least important sire lines that went back to dogs not found as often in modern pedigrees, it has become almost impossible to find “show” dogs that are not linebred. As a result of moderately strong linebreeding, we find such problems as immune system deficiencies. These are not prejudicially singled out; they are too representative of many, many dogs in the same boat. When “everybody” breeds to the same small number of dogs or bloodlines, these types of weaknesses are what you’ll get. Whether “new” or not, breeds on the edges of what some consider “purebred” are faced with the challenge to keep enough diversity to prevent problems from becoming so deeply imbedded in the gene pool that there is almost no correction possible.

Some 80% of Dobermans are either "affected" by, or "carriers" of, the genes for von Willebrand’s Disease (vWD), which means that purebred Doberman fanciers are in a real bind, as elimination of all those dogs would mean disaster for the breed. Whenever possible, breeders should outcross! One common route to inbreeding is the widespread use of a single popular national champion or a handful of top champions to the exclusion of other good but less-highly placed competition dogs. While you may be increasing the chances of getting a dog that has some of the same obvious (probably dominant or homozygous) desirable qualities, you are at the same time increasing the concentration of so far hidden recessives, many or most of which are bad for the breed. When most people flock to the leaders for stud service, these bad genes are concentrated as well, and the good genes that an unused dog could have contributed may be lost forever. The undesirable recessives previously hidden in the lines will soon become glaring problems, impossible to ignore and difficult to get rid of.